<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //作用域链：函数使用变量的时候，采用最近原则

        //案例一： 结果为几？
        var num =456;
        function f1() {
            var num =123;
            function f2() {
                var num = 0;
                console.log(num);//站在目标出发，一层一层往外查找
            }
            f2();

        }
        f1();




        //案例二：结果是几？

        var a =1;

        function fn1() {
            var a=2;
            var b ='22';
            fn2();


            
            function fn2() {
                var a = 3;
                fn3();

                

                function fn3() {
                    var a = 4;
                    console.log(a); //a的值 ?
                    console.log(b); //b的值 ?
                }
            }
        }
        
    </script>
</body>
</html>